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A frequency selective atom interferometer magnetometer

Published in:
J. Mod. Opt., Vol. 61, No. 1, 2014, pp. 61-71.
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Summary

In this article, we discuss the magnetic-field frequency selectivity of a time-domain interferometer based on the number and timing of intermediate pi pulses. We theoretically show that by adjusting the number of pi pulses and the pi-pulse timing, we can control the frequency selectivity of the interferometer to time varying and DC magnetic fields. We present experimental data demonstrating increased coherence time due to bandwidth filtering with the inclusion of a pi pulse between the initial and final pi/2 pulses, which mitigates sensitivity to low frequency magnetic fields.
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Summary

In this article, we discuss the magnetic-field frequency selectivity of a time-domain interferometer based on the number and timing of intermediate pi pulses. We theoretically show that by adjusting the number of pi pulses and the pi-pulse timing, we can control the frequency selectivity of the interferometer to time varying...

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Quantum information processing using quasiclassical electromagnetic interactions between qubits and electrical resonators

Published in:
New J. Phys., Vol. 15, 2013, 123011.
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Summary

Electrical resonators are widely used in quantum information processing, by engineering an electromagnetic interaction with qubits based on real or virtual exchange of microwave photons. This interaction relies on strong coupling between the qubits' transition dipole moments and the vacuum fluctuations of the resonator in the same manner as cavity quantum electrodynamics (QED), and has consequently come to be called 'circuit QED' (cQED). Great strides in the control of quantum information have already been made experimentally using this idea. However, the central role played by photon exchange induced by quantum fluctuations in cQED does result in some characteristic limitations. In this paper, we discuss an alternative method for coupling qubits electromagnetically via a resonator, in which no photons are exchanged, and where the resonator need not have strong quantum fluctuations. Instead, the interaction can be viewed in terms of classical, effective 'forces' exerted by the qubits on the resonator, and the resulting resonator dynamics used to produce qubit entanglement are purely classical nature. We show how this type of interaction is similar to that encountered in the manipulation of atomic ion qubits, and we exploit this analogy to construct two-qubit entangling operations that are largely insensitive to thermal or other noise in the resonator, and to its quality factor. These operations are also extensisble to larger numbers of qubits, allowing interactions to be selectively generated among any desired subset of those coupled to a single resonator. Our proposal is potentially applicable to a variety of physical qubit modalities, including superconducting and semiconducting solid-state qubits, trapped molecular ions, and possibly even electron spins in solids.
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Summary

Electrical resonators are widely used in quantum information processing, by engineering an electromagnetic interaction with qubits based on real or virtual exchange of microwave photons. This interaction relies on strong coupling between the qubits' transition dipole moments and the vacuum fluctuations of the resonator in the same manner as cavity...

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Ultrawideband superstrate-enhanced substrate-loaded array with integrated feed

Published in:
IEEE Trans. Antennas Propag., Vol. 61, No. 11, November 2013, pp. 5802-7.
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Summary

A superstrate-enhanced substrate-loaded array (SESLA) with an integrated feed is presented. The design allows for a practical implementation of the SESLA, a concept previously presented by the authors for realizing extremely wideband (> 10 : 1) low-profile arrays. Specifically, the feed provides unbalanced to balanced transformation allowing the balance-fed SESLA to be excited with a 50 omega unbalanced line. The resulting array/feed combination is matched across a 13.9 : 1 bandwidth (infinite array, V SW R less than or equal to 2.4). When scanned to 45 degrees in the E-, H-, and D-planes, the unit cell operates across a 13.3 : 1 bandwidth using a relaxed matching criterion of V SW R less than or equal to 3. The design is validated through extensive measurement of an 8x8 prototype array.
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Summary

A superstrate-enhanced substrate-loaded array (SESLA) with an integrated feed is presented. The design allows for a practical implementation of the SESLA, a concept previously presented by the authors for realizing extremely wideband (> 10 : 1) low-profile arrays. Specifically, the feed provides unbalanced to balanced transformation allowing the balance-fed SESLA...

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Flux-charge duality and topological quantum phase fluctuations in quasi-one-dimensional superconductors

Published in:
New J. Phys., Vol. 15, 2013, 105017.
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Summary

It has long been thought that macroscopic phase coherence breaks down in effectively lower-dimensional superconducting systems even at zero temperature due to enhanced topological quantum phase fluctuations. In quasi-one-dimensional wires, these fluctuations are described in terms of 'quantum phase-slip' (QPS): tunneling of the superconducting order parameter for the wire between states differing by plus or minus 2 pi in their relative phase between the wire's ends. Over the last several decades, many deviations from conventional bulk superconducting behavior have been observed in ultra-narrow superconducting nanowires, some of which have been identified with QPS. While at least some of the observations are consistent with existing theories for QPS, other observations in many cases point to contradictory conclusions or cannot be explained by these theories. Hence, our understanding of the nature of QPS, and its relationship to the various observations, has remained incomplete. In this paper we present a new model for QPS which takes as its starting point an idea originally postulated by Mooij and Nazarov (2006 Nature Phys. 2 169): that flux-charge duality, a classical symmertry of Maxwell's equations, can be used to relate QPS to the well-known Josephson tunneling of Cooper pairs. Our model provides an alternative, and qualitatively different, conceptual basis for QPS and the phenomena which arise from it in experiments, and it appears to permit for the first time a unified understanding of observations across several different types of experiments and materials systems.
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Summary

It has long been thought that macroscopic phase coherence breaks down in effectively lower-dimensional superconducting systems even at zero temperature due to enhanced topological quantum phase fluctuations. In quasi-one-dimensional wires, these fluctuations are described in terms of 'quantum phase-slip' (QPS): tunneling of the superconducting order parameter for the wire between...

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A least mean squares approach of iterative array calibration for scalable digital phased array radar panels

Published in:
2013 IEEE Int. Symp. On Phased Array Systems and Technology, 15-18 October 2013.
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Summary

This paper describes a semiautonomous approach to calibrate a phased array system, with particular use on an S-band aperture that is being developed at MIT Lincoln Laboratory. Each element of the array is controlled by an independent digital phase shifter, whose control signal may be uniquely defined. As active electronically steerable arrays (AESAs) continually evolve towards mostly digital paradigms that will support real-time computing, as opposed to look-up table approaches, then adaptive calibration approaches may be pursued for maximum AESA performance. This calibration work is being completed as one component of Lincoln Laboratory's effort within the multifunction phased array radar (MPAR) initiative.
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Summary

This paper describes a semiautonomous approach to calibrate a phased array system, with particular use on an S-band aperture that is being developed at MIT Lincoln Laboratory. Each element of the array is controlled by an independent digital phase shifter, whose control signal may be uniquely defined. As active electronically...

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A method for improved cross-pol isolation based on the use of auxiliary elements

Published in:
2013 IEEE Int. Symp. On Phased Array Systems and Technology, 15-18 October 2013.

Summary

This paper describes a method to answer the following questions: can several of the elements of a phased array be employed as auxiliary (AUX) elements and how can the phase of each be adjusted so that the (1) cross-polarization (cross-pol) isolation is minimized to 40 dB, (2) the sidelobe levels of the main lobe are minimally impacted, and (3) the width and height of the main lobe are minimally impacted? This calibration work is being completed as one component of Lincoln Laboratory's effort within the multifunction phased array radar (MPAR) initiative. Devoting a few of the elements to serve as the AUX channels to specifically operate to mitigate the effects of the cross-pol influence, the distributed sidelobe levels will not suffer much impact; yet, the impact of the AUX elements will have deepened the cross-pol isolation at the peak of the co-polar beam can occur because the AUX elements can achieve a high degree of narrowband angular resolution.
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Summary

This paper describes a method to answer the following questions: can several of the elements of a phased array be employed as auxiliary (AUX) elements and how can the phase of each be adjusted so that the (1) cross-polarization (cross-pol) isolation is minimized to 40 dB, (2) the sidelobe levels...

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Dual-polarization challenges in weather radar requirements for multifunction phased array radar

Published in:
2013 IEEE Int. Symp. On Phased Array Systems and Technology, 15-18 October 2013.
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Summary

This paper summarizes the challenges in achieving (and even specifying) the antenna polarization accuracy requirements for the Multifunction Phased Array Radar (MPAR) and the progress that has been made towards meeting these requirements through demonstrations and theoretical investigations.
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Summary

This paper summarizes the challenges in achieving (and even specifying) the antenna polarization accuracy requirements for the Multifunction Phased Array Radar (MPAR) and the progress that has been made towards meeting these requirements through demonstrations and theoretical investigations.

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Low cost phased array radar for applications in engineering education

Published in:
2013 IEEE Int. Symp. On Phased Array Systems and Technology, 15-18 October 2013.

Summary

Hands-on instruction in engineering education is beneficial to the development of a workforce that understands the complexity of building radar systems. Unfortunately, building phased array systems tends to be too costly to allow student access to the hardware necessary for developing these skills. This paper presents a low cost phased array based on a time-domain multiplexed, multiple-input, multiple-output (TDM-MIMO) approach that has been built for education. This array has been utilized in several free courses held at the Massachusetts Institute of Technology during the Independent Activity Period (IAP) between semesters. Students have built, tested, and taken home a number of these radars and continue to operate these on their own, either for recreation or as part of their undergraduate research activities.
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Summary

Hands-on instruction in engineering education is beneficial to the development of a workforce that understands the complexity of building radar systems. Unfortunately, building phased array systems tends to be too costly to allow student access to the hardware necessary for developing these skills. This paper presents a low cost phased...

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Multi-lithic phased array architecture for airborne sense and avoid radar

Summary

Transmit and receive Ku-band phased array designs are described for testing an airborne sense and avoid radar. The arrays are small with a size of 24 cm x 9 cm and operate from 13 to 17 GHz with electronic scanning from plus of minus 45 degrees in azimuth and plus of minus 30 degrees in elevation. A novel design architecture allows the use of multiple multilayered printed circuit boards and simple air cooling.
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Summary

Transmit and receive Ku-band phased array designs are described for testing an airborne sense and avoid radar. The arrays are small with a size of 24 cm x 9 cm and operate from 13 to 17 GHz with electronic scanning from plus of minus 45 degrees in azimuth and plus...

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On the development of a tileable LRU for the NextGen surveillance and weather radar capability program

Published in:
2013 IEEE Int. Symp. On Phased Array Systems and Technology, 15-18 October 2013.

Summary

MIT Lincoln Laboratory is working towards the development of a tileable radar panel to satisfy multimission needs. A combination of custom and commercial off-the-shelf (COTS) Monolithic Microwave Integrated Circuits (MMICs) have been developed and/or employed to achieve the required system functionality. The integrated circuits (ICs) are integrated into a low cost T/R module compatible with commercial printed circuit board (PCB) manufacturing. Sixty-four of the transmit/receive (T/R) modules are integrated onto the aperture PCB in an 8x8 lattice. In addition to the T/R elements, the aperture PCB incorporates transmit and receive beamformers, power and logic distribution, and radiating elements. The aperture PCB is coupled with a backplane PCB to form a panel, the line replaceable unit (LRU) for the multifunction phased array radar (MPAR) initiative. This report summarizes the evaluation of the second iteration LRU aperture PCB and T/R element. Support fixturing was developed and paired with the panel to enable backplane functionality sufficient to support the test objective.
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Summary

MIT Lincoln Laboratory is working towards the development of a tileable radar panel to satisfy multimission needs. A combination of custom and commercial off-the-shelf (COTS) Monolithic Microwave Integrated Circuits (MMICs) have been developed and/or employed to achieve the required system functionality. The integrated circuits (ICs) are integrated into a low...

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